Driving circuit of a liquid crystal display panel

ABSTRACT

A driving circuit of a liquid crystal display panel includes a substrate, a plurality of driver IC chips located on the substrate, a current supplier, and a first conductive wire set. The first conductive wire set has a plurality of conductive wire segments for connecting the driver IC chips in parallel to the current supplier. Furthermore, the conductive wire segments each have a form, such that paths formed of the conductive wire segments from the current supplier to the respective driver IC chips have an equal resistance, and, accordingly, each of the driver IC chips obtain the same input voltage. Hence, a problem of band mura is avoided.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional application of and claimspriority to U.S. patent application Ser. No. 11/161,988, filed on Aug.24, 2005, and entitled “Driving circuit of a liquid crystal displaypanel” the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a driving circuit of a liquid crystaldisplay panel, and more particularly to a driving circuit, in which thedriver IC chips each obtain an approximately identical input voltage.

2. Description of the Prior Art

A thin film transistor liquid crystal display (TFT-LCD) panel utilizesmany thin film transistors (TFTs), in conjunction with other elementssuch as capacitors and bonding pads, arranged in a matrix as switchesfor driving liquid crystal molecules to produce brilliant images.Generally, the conventional TFT-LCD panel includes an upper substratehaving a color filter, a lower substrate, and liquid crystal materialsbetween the substrates. The lower substrate comprises a plurality ofscan lines (gate lines) and a plurality of signal lines (source lines)orthogonally cross over the scan lines. At least one TFT is located nearthe crossover of the scan line and the signal line, as a switch devicefor the pixel.

Please refer to FIG. 1. FIG. 1 is a schematic diagram showing astructure of a conventional liquid crystal display panel. As shown inFIG. 1, a TFT-LCD panel 10 comprises a substrate 12 and an X-printingwiring board 14. In addition, the TFT-LCD panel 10 comprises a pluralityof flexible printing circuit boards (FPC) 16 for electrically connectingthe X-printing wiring board 14 and the substrate 12. Source driver ICchips 18 are positioned on the side region of the substrate 12 connectedto the FPC 16 and electrically connecting to the FPC 16.

A plurality of scanning lines S₁, S₂, . . . , and S_(m) and a pluralityof signal lines D₁, D₂, . . . , and D_(n) are positioned on thesubstrate 12. The scanning lines S₁, S₂, . . . , and S_(m) orthogonallycross over the signal lines D₁, D₂, . . . , and D_(n) to define a pixelmatrix (not shown) in an active region 19 on the substrate 12. Inaddition, the substrate 12 further comprises an outer lead bondingregion (OLB) 20 and a gate driving circuit 22 positioned in the OLB 20.The gate driving circuit 22 comprises driver IC chips 22 a and 22 b, foroutputting switch/addressing signals to the scanning lines S₁, S₂, . . ., and S_(m). The source driver IC chips 18 are used for outputting imagedata signals to the signal lines D₁, D₂, . . . , and D_(n). The driverIC chips 18, 22 a, and 22 b are formed on the surface of the substrate12 by chip-on-glass (COG) technology. The driving circuit 22 comprises aplurality of conductive wires 24 for electrically connecting the driverIC chips 22 a and 22 b in series. The conductive wires 24 are formeddirectly on the surface of the substrate 12, and such design is calledwiring on array (WOA).

When the liquid crystal display panel 10 is operated, a driving voltagefor a controlling signal 28 is output from the X-printing wiring board14, as shown in FIG. 1, passes through the FPC 16 and the conductivewires 24, and inputs to the driver IC chips 22 a and 22 b. Finally, thedriver IC chips 22 a and 22 b output switch/addressing signals to thescanning lines S₁, S₂, . . . , and S_(m) according to the input voltage.In addition, as shown in FIG. 2, the driver IC chips 22 a and 22 b areelectrically connected in series. Since the conductive wires 24 produceresistances R₁ and R₅, the driver IC chip 22 a has an inner resistanceR₃, and contact points of the elements produce resistances R₂, R₄, andR₆, there is a relatively large total resistance.

The width of the conductive wires is broadened as wide as possible toreduce the resistance in traditional wiring techniques. The conductivewires connect ICs from the first IC to the last IC in series. However,the interface impedance between metal lines and ITO layer may be as highas 200Ω. Thus, the difference of the wiring resistance between the firstIC and the wiring resistance of the last IC will be as high as 500Ω.Therefore, the driver IC chips 22 a and 22 b receive different inputvoltages when a voltage of the controlling signal 28 is applied to them,and in turn the output voltages from the driver IC chips 22 a and 22 bare different. The received voltage difference between the first IC andthe last IC may be about 0.3V which leads the liquid crystal displaypanel 10 to have a band mura problem and an uneven brightness, resultinga poor display quality. As shown in FIG. 3, the display 30 isschematically shown to have a band mura.

Please refer to FIG. 4 illustrating a well known method to inhibit theband mura by adding a resistor 31 at the signal input position on theprinted circuit board, such that an input signal would have anoscillating distortion with an amplitude larger than the voltagedifference caused by the wiring impedance to obscure the band muraphenomenon. However, the power consumption of the entire driving circuitwould be increased in such method.

Therefore, a good driving circuit of a liquid crystal display panel isstill needed for giving each driver IC chip an approximately identicalinput voltage to avoid band mura phenomenon.

SUMMARY OF THE INVENTION

An object of the claimed invention is to provide a driving circuit of aliquid crystal display panel, such that band mura caused by differentinput voltages on the driver IC chips can be avoided.

The driving circuit of a liquid crystal display panel according to theclaimed invention comprises a substrate, a plurality of driver IC chipspositioned on the substrate, a current supplier, and a first conductivewire set. The first conductive wire set comprises a plurality ofconductive wire segments for connecting the driver IC chips in parallelto the current supplier. The conductive wire segments each have a form,such that paths formed of the conductive wire segments from the currentsupplier to the respective driver IC chips have an equal resistance andeach of the driver IC chips obtain a same input voltage.

With respect to another aspect of the present invention, the drivingcircuit of a liquid crystal display panel according to the presentinvention comprises a substrate, a plurality of driver IC chipspositioned on the substrate, a current supplier, and a first conductivewire set comprising a conductive wire for electrically connecting thedriver IC chips in parallel to the current supplier.

In the driving circuit according to the claimed invention, a pluralityof driver IC chips are electrically connected to a current supplier in aparallel layout. Each conductive wire segment may further have adesigned shape such that the resistance of each conductive path from thedriver IC chip to the current supplier is almost identical, andtherefore, each of the driver IC chips obtains an identical inputvoltage, to resolve the problem of band mura. In addition, the powerconsumption will not be accordingly increased. The display quality ofliquid crystal display panel is hence improved.

These and other objectives of the present invention will no doubt becomeobvious to those of ordinary skill in the art after reading thefollowing detailed description of the preferred embodiment that isillustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a structure of a conventionalliquid crystal display panel.

FIG. 2 is a schematic diagram showing resistances produced in a drivingcircuit of a conventional liquid crystal display panel.

FIG. 3 is a schematic diagram showing a band mura in a conventionalliquid crystal display panel.

FIG. 4 is a schematic diagram showing a conventional technique toresolve a band mura problem.

FIG. 5 is a schematic diagram showing a driving circuit of a liquidcrystal display panel according to the present invention.

FIG. 6 is a schematic diagram showing a driving circuit of a liquidcrystal display panel of one embodiment according to the presentinvention.

FIG. 7 is a schematic diagram showing a structure of a conductive wireset in the driving circuit of a liquid crystal display panel accordingto the present invention.

FIG. 8 is a table showing an example of the conductive wire segment A,B, and C combination in the present invention.

FIG. 9 is a table showing another example of the conductive wire segmentA, B, and C combination in the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 5. FIG. 5 is a schematic diagram showing a drivingcircuit of a liquid crystal display panel according to the presentinvention. As shown in FIG. 5, the driving circuit 32 of a liquidcrystal display panel according to the present invention comprises a TFTsubstrate 33, two driver IC chips 34 and 36 positioned on the TFTsubstrate 33, a current supplier 42, and a conductive wire set 40 forconnecting the driver IC chips 34 and 36 in parallel to the currentsupplier 42.

The conductive wire set 40 comprises a plurality of conductive wiresegments. The form of each conductive wire segment is not particularlylimited, as long as it can be laid out on the substrate and has thedesired resistance such that driver IC chips arranged in parallel caneach obtain an approximately identical input voltage. In FIG. 5, theconductive wire set 40 comprises a main wire segment 38 and two branchwire segments 39 a and 39 b. One end of the main wire segment isconnected to the current supplier 42, and each of the branch wiresegments 39 a and 39 b respectively connects the other end of the mainwire segment 38 with one of the driver IC chips 34 and 36. Although theconductive wire segments are called as “main” or “branch”, the shape orsize, for example, length, width, or thickness, is not formed as beingprincipal or subsidiary, as long as the conductive wire segments canconnect each of the driver IC chips 34 and 36 in parallel to the currentsupplier. Therefore, the shape or size of conductive wire segments mayhave many variations and combinations that result in paths from thecurrent supplier 42 to the driver IC chip 34 and from the currentsupplier 42 to the driver IC chip 36, having an approximately identicalresistance. That is, the voltage drops for the respective paths from thecurrent supplier 42 to the driver IC chips 34 and 36 should beapproximately identical, thereby each driver IC chip can obtain asubstantially identical input voltage.

The conductive wire may comprise conductive material, such as, metal,alloy, or indium tin oxide (ITO). The metal or alloy may be, but notlimited to, aluminum, chromium, molybdenum, aluminum-neodymium (AlNd),and the like.

Please refer to FIG. 6 showing an application of the driving circuitaccording to the present invention to a liquid crystal display panel 43.The liquid crystal display panel 43 comprises a substrate 33 and aprinted circuit board 44. A plurality of scanning lines S₁, S₂, . . . ,and S_(m) and a plurality of signal lines D₁, D₂, . . . , and D_(n) arepositioned on the substrate 33, m and n being a positive integer, todefine a pixel matrix (not shown) in an active region 35 on thesubstrate 33. In addition, the substrate 33 further comprises an OLB 37and gate driver IC chips 34 and 36 and conductive wire sets 40 and 50 onthe OLB 37. The liquid crystal display panel 43 further comprises aplurality of flexible printed circuit board (FPC) 46 for electricallyconnecting the printed circuit board 44 and the substrate 33. Sourcedriver IC chips 48 are positioned on the OLB 37 at the side of thesubstrate 33 connecting with the FPC 46. Current is output by a currentsupplier from the printed circuit board 44 and passes to the FPC 46.

The conductive wire set may be fabricated simultaneously with thefabrication of scanning lines on the substrate and comprise a samematerial as the scanning lines, fabricated simultaneously with thefabrication of signal lines on the substrate and comprise a samematerial as the signal lines, or fabricated simultaneously with thefabrication of pixel electrodes on the substrate and comprise a samematerial as the pixel electrodes. When the wires are used for conductinggate driver IC chips, it is preferably that the wires are fabricatedsimultaneously with the fabrication of scanning lines and comprise asame material as the scanning lines for convenience and having arelatively small resistance.

Please refer to FIG. 6 again. The driving circuit of a liquid crystaldisplay panel according to the present invention may comprise aplurality of conductive wire sets, for example, two conductive wire sets40 and 50. The conductive wire set 40 is described in detailed in theabove description. The conductive wire set 50 is disposed in a similarway to the conductive wire set 40 and comprises a plurality ofconductive wire segments, independent of the conductive wire set 40. Theconductive wire set 50 may be the same as or different from theconductive wire set 40. The conductive wire set 50 must connect thedriver IC chips 34 and 36 in parallel to the current supplier 42 andallow voltage drops for the respective paths from the current supplier42 to the driver IC chips 34 and 36 to be approximately identical.Therefore, the shape or size of conductive wire segments may have manyvariations and combinations. In the embodiment shown by FIG. 6, theconductive wire set 40 may be set to carry an on-state current and theconductive wire set 50 may be set to carry an off-state current.

It is known that the resistance of a conductive wire is proportional tothe length of the conductive wire per se, and inversely proportional tothe cross section area of the conductive wire. Accordingly, theresistance of a conductive wire can be obtained by a simulativecalculation. Therefore, in the present invention, for a predeterminedresistance, there are may combinations for the shapes, such as thelength, width, and thickness, of conductive wire segments in theconductive wire set to approach the desired resistance. Please refer toFIG. 7 showing a structure of a conductive wire set in the drivingcircuit of a liquid crystal display panel of an embodiment according tothe present invention. The conductive wire set comprises conductive wiresegments A, B, and C. One end of the conductive wire segment B connectsto the conductive wire segment A and the other end connects to thedriver IC chip 34. One end of the conductive wire segment C connects tothe conductive wire segment A and the other end connects to the driverIC chip 36. Two examples of possible combinations for the length, width,thickness and material for conductive wire segments A, B, and C areshown in tables in FIGS. 8 and 9, respectively. As the combinations ofthe conductive wire segments shown in the tables, they are suitable tobe a conductive wire set for TFT on-state voltage (V_(gg)) or off-statevoltage (V_(ee)) transmission.

Furthermore, the present invention is not limited to the above-mentioneddriving circuit for outputting switch/addressing signals to the scanninglines, and a driving circuit for outputting image information signals tothe signal lines is also encompassed.

As compared to the conventional method, in which a resistor is added atthe signal input position on the printed circuit board to make the inputsignal to have an oscillating distortion to resolve the band muraphenomenon, in the present invention, an additional resistor is notneeded, thus the power consumption is not increased. In the presentinvention, the resistance existing on the wiring path from each driverIC chip to the current supplier is approximately identical, thus eachdriver IC chip receives an approximately identical voltage to avoid theband mura problem and the display quality is improved.

Those skilled in the art will readily observe that numerousmodifications and alterations of the device and method may be made whileretaining the teachings of the invention. Accordingly, the abovedisclosure should be construed as limited only by the metes and boundsof the appended claims.

1. A driving circuit of a liquid crystal display panel, comprising: asubstrate; a plurality of driver IC chips positioned on the substrate; acurrent supplier; and a first conductive wire set comprising aconductive wire for electrically connecting the driver IC chips inparallel to the current supplier.
 2. The driving circuit of claim 1,wherein the conductive wire and the driver IC chips are electricallyconnected by a plurality of conductive wire segments, and the conductivewire segments each have a form, such that paths formed of the conductivewire segments from the current supplier to the respective driver ICchips each have an equal resistance and each of the driver IC chipsobtain a same input voltage.
 3. The driving circuit of claim 1, whereinthe first conductive wire set comprises a metal layer, alloy layer, orindium tin oxide (ITO) layer.
 4. The driving circuit of claim 1, whereinthe substrate further comprises a plurality of scanning lines and aplurality of signal lines.
 5. The driving circuit of claim 4, whereinthe driver IC chips output switch/addressing signals to the scanninglines.
 6. The driving circuit of claim 4, wherein the driver IC chipsoutput image information signals to the signal lines.
 7. The drivingcircuit of claim 4, wherein the first conductive wire set comprises asame material as the scanning lines.
 8. The driving circuit of claim 4,wherein the first conductive wire set comprises a same material as thesignal lines.
 9. The driving circuit of claim 1, further comprises asecond conductive wire set comprising a conductive wire for electricallyconnecting the driver IC chips in parallel to the current supplier. 10.The driving circuit of claim 9, wherein the conductive wire included inthe second conductive wire set and each of the driver IC chips areelectrically connected by a conductive wire segment, and the conductivewire segments each have a form, such that paths formed of the secondconductive wire segments from the current supplier to the respectivedriver IC chips have an equal resistance and each of the driver IC chipsobtain a same input voltage.
 11. The driving circuit of claim 9, whereinthe first conductive wire set carries a thin film transistor on-statecurrent and the second conductive wire set carries a thin filmtransistor off-state current.
 12. The driving circuit of claim 9,wherein the second conductive wire set comprises a metal layer, alloylayer, or indium tin oxide (ITO) layer.
 13. The driving circuit of claim9, wherein the substrate further comprises a plurality of scanning linesand a plurality of signal lines.
 14. The driving circuit of claim 13,wherein the driver IC chips output switch/addressing signals to thescanning lines.
 15. The driving circuit of claim 13, wherein the driverIC chips output image information signals to the signal lines.
 16. Thedriving circuit of claim 13, wherein the second conductive wire setcomprises a same material as the scanning lines.
 17. The driving circuitof claim 13, wherein the second conductive wire set comprises a samematerial as the signal lines.